A new type of photovoltaic (PV) module includes various silicon wafers that are electrically connected to a conductive backsheet or member. Unlike traditional designs, this type of photovoltaic cell employs laser drilled vias connecting the front surface carrier collector junction to an electrode grid on the back surface. Therefore, the back contact silicone cells use only coplanar contacts on the back surface (as described in U.S. Pat. Nos. 5,468,652 and 5,951,786, both to Gee) and avoid the difficulty in making the front to back lead attachment. This coplanar connection allows all the cells in a photovoltaic module to be electrically connected in a single step. Collections of these cells are referred to as a monolithic module assembly (MMA).
Copper (Cu) has been used as the electrode for the backsheet assembly for back contact photovoltaic cells. Since copper is expensive, there is a need to use less expensive conductive materials. The same is true for other situations where a laser patterned conductive element is preferred. Aluminum is desired for many backsheet contact photovoltaic applications due to its relatively low cost.
However, a naturally occurring oxide layer exists on the surface of aluminum. The oxide layer exhibits relatively high electrical resistance. And so, if electrical connections are to be made to the aluminum electrode(s), the oxide layer must be removed.
Although various methods are known for removing oxide layers from electrically conductive members, many of those methods are expensive or time consuming and treat an entire sheet of aluminum foil. Another consequence associated with removal of oxide from aluminum is that after removal of an oxide layer, that layer quickly re-oxidizes even under ambient conditions. Furthermore, aluminum electrodes rapidly re-oxidize if subjected to high temperatures and/or high humidity. Accordingly, a need exists for a method by which aluminum based electrodes, and particularly those used in photovoltaic assemblies, can be economically prepared or processed to be resistant to oxidation yet be electrically conductive.